It is the objective of this project to maintain a Pathology Reference Center and Repository and nine regional centers for the purpose of rendering diagnostic and research support to cooperative clinical studies pertaining to the therapy of malignant lymphomas. The Pathology Reference Center and the regional centers are headed by pathologists who have specialized in the diagnosis and study of neoplastic diseases of the lymphoreticular system and are making a joint effort to improve and refine the criteria for diagnosis and classification of these neoplastic diseases, thus to assure the validity of the therapeutic results reported or to be reported by their clinical colleagues engaged in therapeutic clinical studies. A number of ancillary research projects closely related to the primary aim represent endeavors to supplement the work initiated under the auspices of the Hodgkin's disease clinical therapeutic trial study and the Lymphoma Clinical Studies. BIBLIOGRAPHIC REFERENCES: Burke, J. S., Mackay, B., and Rappaport, H.: Hairy cell leukemia (leukemic reticuloendotheliosis). 11. Ultrastructure of the spleen. Cancer 37:2267-2274, 1976. Nathwani, B. N., Kim, H., and Rappaport, H.: Malignant lymphoma, lymphoblastic. Cancer 38:964-983, 1976.